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The protocol is defined as : Bob want to send message to one of his friends say $k$ friends , he does not want his others friends (except one whom he want to send message ) to tell who is targeted recipient. Here public key of all the participants are known. I read this is anonymous public key encryption in some paper ,but this paper said hat ElGamal public-key encryption is able to provide this type of encryption but RSA cannot . I thought both can able to provide , my question is can we do some mathematical analysis (probabilistic one) to show that ElGamal public-key encryption able to provide this type of encryption but not RSA. Can somebody share me some resources where detail analysis is done.

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  • $\begingroup$ I believe that RSA can provide this type of destination anonymity, given that a) everyone picks their public key modulus fairly close, e.g. in the range $[2^{2048} (1 - 2^{-256}), 2^{2048}]$ and b) you use a nondeterministic padding type (so the attacker can't deduce anything from the Jacobi symbol). (a) is fairly easy to do (we generally don't bother, but we could if there were need), (b) is standard practice anyways... $\endgroup$
    – poncho
    May 3, 2021 at 2:41
  • $\begingroup$ @poncho here we want to analyze any middle man say Oscar seeing cipher text should not get to know targeted recipient , how can we say ElGamal preservers that and RSA not. $\endgroup$
    – Sam
    May 3, 2021 at 3:26

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